In humans, the effects of current feeding practices in infancy on the later development of obesity are unclear. Cereal feeding may theoretically lead to increased caloric intake and subsequently, to decreased formula consumption. Replacement of nutritionally-balanced formula by carbohydrate-rich cereal may promote storage of fat rather than growth of lean body mass. In addition, cereals, which are a good source of soluble fiber, may limit cholesterol absorption in the gut, which might indirectly lead to increased cholesterol synthesis in the liver. The purpose of this project is to study body composition and lipid metabolism in infants randomized to either exclusive formula feeding from birth to six months of age (group F), or to the same formula feeding until six months of age but with cereal supplementation from four months of age (group F-C). We hypothesize that fat mass, but not lean body mass (measured by total body electrical conductance) will be greater in the F-C group, as compared to the F group at six months of age and at one year of age. In addition, we hypothesize that at six months and one year of age, differences in weight between sexes will be explained by greater lean body mass accretion in males than in females; that introduction of cereal to the infant's diet will lead to increased endogenous cholesterol synthesis rate (measured using a deuterated water label) and decreased LDL-receptor activity (measured using a lymphocyte LDL-receptor assay). Furthermore, we hypothesize that the above changes in body composition and lipid metabolism will still be present at one year of age when the two groups no longer differ by diet, indicative of biological imprinting. This study should further our understanding of the effect of early infant nutrition on body composition and lipid metabolism.